I have two tables: one with points, the other with polys.
CREATE TABLE `points` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`point` point NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM;
CREATE TABLE `ranges` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`poly` polygon NOT NULL,
PRIMARY KEY (`id`),
SPATIAL KEY `poly` (`poly`)
) ENGINE=MyISAM;
I want to join ranges to points on points inside polys. Queries look simple:
SELECT *
FROM points
LEFT JOIN ranges
ON MBRCONTAINS(poly, point)
WHERE points.id = 2;
This query works fast and uses indexes, part of explain:
table | type | possible_keys | key | key_len ranges | range | poly | poly | 34
But, when I try to join with several rows from table points:
SELECT *
FROM points
LEFT JOIN ranges
ON MBRCONTAINS(poly, point)
WHERE points.id IN (1,2,3);
everything breaks down:
+----+-------------+------------+-------+---------------+---------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+-------+---------------+---------+---------+------+--------+-------------+ | 1 | SIMPLE | points | range | PRIMARY | PRIMARY | 4 | NULL | 3 | Using where | | 1 | SIMPLE | ranges | ALL | poly | NULL | NULL | NULL | 155183 | | +----+-------------+------------+-------+---------------+---------+---------+------+--------+-------------+
Adding FORCE INDEX (poly) does not help.
Sample data to test queries (sorry, only php version, I'm not common with SQL procedures):
//points
for($i=0;$i<=500;$i++) {
$point = mt_rand();
mysql_query('INSERT INTO points (point) VALUES (POINTFROMWKB(POINT('.$point.', 0)))');
}
$qty = 20000;
$max = mt_getrandmax();
$add = $max / $qty
$end = 0;
//polys
while($end < $max) {
$start = $end;
$end = mt_rand($start, $start + $add);
mysql_query('INSERT INTO ranges (poly) VALUES (
GEOMFROMWKB(POLYGON(LINESTRING(
POINT('.$start.', -1),
POINT('.$end.', -1),
POINT('.$end.', 1),
POINT('.$start.', 1),
POINT('.$start.', -1)
)))
)');
}
I believe that it's because MySQL doesn't support merging spatial indexes. Not sure if it's still true but I've read it somewhere in the past. If you have an OR statement, then the spatial indexes are not used
In your case, where are you doing points.id = 1, that's a straight select with one result returned that gets used in the mbrcontains. That uses the index.
When you add points.in (1,2,3), that returns 3 results and each needs to be mapped to the ranges table, therefore not working
result
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE points range PRIMARY PRIMARY 4 NULL 3 100.00 Using where
1 SIMPLE ranges ALL poly NULL NULL NULL 6467418 100.00
You can simplify your test without the the point table by doing this: SELECT * FROM ranges where mbrcontains( poly, GEOMFROMWKB(POINT(0, 0)))
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE ranges range poly poly 34 NULL 1 100.00 Using where
And now this; SELECT * FROM ranges where mbrcontains( poly, GEOMFROMWKB(POINT(0, 0))) OR mbrcontains( poly, GEOMFROMWKB(POINT(10, 10)))
result
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE ranges ALL poly NULL NULL NULL 6467418 100.00 Using where
See that in the second case, you are not using index and just scanning.
You could force the query to use index by creating UNION for each specific point but I am not sure if that's going to be faster. I did some tests locally and it was a bit slower than your first query.
EXPLAIN EXTENDED
SELECT *
FROM points
FORCE INDEX (PRIMARY )
LEFT JOIN ranges
FORCE INDEX ( poly ) ON mbrcontains( poly, point )
WHERE points.id = 1
UNION DISTINCT
SELECT *
FROM points
FORCE INDEX (PRIMARY )
LEFT JOIN ranges
FORCE INDEX ( poly ) ON mbrcontains( poly, point )
WHERE points.id = 2
UNION DISTINCT
SELECT *
FROM points
FORCE INDEX (PRIMARY )
LEFT JOIN ranges
FORCE INDEX ( poly ) ON mbrcontains( poly, point )
WHERE points.id = 3
result
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY points const PRIMARY PRIMARY 4 const 1 100.00
1 PRIMARY ranges range poly poly 34 NULL 1 100.00 Using where
2 UNION points const PRIMARY PRIMARY 4 const 1 100.00
2 UNION ranges range poly poly 34 NULL 1 100.00 Using where
3 UNION points const PRIMARY PRIMARY 4 const 1 100.00
3 UNION ranges range poly poly 34 NULL 1 100.00 Using where
NULL UNION RESULT <union1,2,3> ALL NULL NULL NULL NULL NULL NULL
I have used successfully similar queries, with only one difference in data model: a spatial key on the points database. In my case:
CREATE TABLE geopoints (
pid int(11) NOT NULL AUTO_INCREMENT,
description varchar(255) NOT NULL DEFAULT '',
geopoint point NOT NULL,
PRIMARY KEY (pid),
SPATIAL KEY geopoint (geopoint)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
And everything went well in queries like this:
SELECT pt.pid, x(geopoint), Y(geopoint), pl.pid, AsText(geopolygon)
FROM geopoints pt INNER JOIN geopolygons pl ON MBRCONTAINS(geopolygon, geopoint)
WHERE pt.pid IN (1,2,4,5) AND pl.pid BETWEEN 1 AND 5;
my two cents,
If all you are dealing with are squares, I would just deal with 4 numbers in your table that can be indexed representing Top, Left, Height, Width, then run your query where your point in question has its "X" coordinate between Left, Left+Width and "Y" coordinate between Top, Top+Height.
You can force MySQL to use the index by encapsulating the subselect in a function.
For example:
DELIMITER $$
DROP FUNCTION IF EXISTS `GetMyPolygon`$$
CREATE DEFINER=`root`@`localhost` FUNCTION `GetMyPolygon`(p POINT) RETURNS INTEGER
BEGIN
DECLARE ret INTEGER;
SET ret = (SELECT range_id FROM ranges WHERE ST_CONTAINS(poly, p) ;
RETURN ret;
END$$
If polygons do not overlap, you can then make:
SELECT *, GetMyPolygon(point) FROM points
If they do overlap, but there a few, you could make a similar function that makes group_concat...
来源：https://stackoverflow.com/questions/8244535/joins-on-spatial-mysql-indexes